Given below is a pedigree chart of a family with five children. It shows the inheritance of attached ear-lobes as opposed to the free ones. The squares represent the male individuals and circles the female individuals. Which one of the following conclusions drawn is correct?

• A

  The parents are homozygous recessive.
• B

  The trait is Y-linked.
• C

  The parents are homozygous dominant.
• Correct answer
  D

  The parents are heterozygous.

Hence, the correct answer is option: 'D'.